Internal combustion engines have substantially higher efficiency at the operating temperature than immediately after starting and thus work optimally in the warmed-up state. It may take a considerable amount of time until the engine has warmed up, especially at low ambient temperatures and with a small load. This problem plays an even more serious role in high-efficiency diesel engines.
Conventionally, in order to warm up the internal combustion engine to operating temperature as quickly as possible, additional electric heating devices heat up the cooling water after starting. A heating resistor is usually provided that is powered directly by the generator and heats up the cooling water in a short time. Conventional cooling water heating devices have a relatively complicated construction, however, and require in particular additional heating elements to heat up the engine.